Measuring apparatus.



M. E. LEEDS. MEASURING APPARATUS. APPLICATION FILED NOV.18, 1912.

1 y 7 5 1 0 Patented May 26, 1914.

M qlln llmlm 14 7M OZJZWENTQR I BY @K A'TTORNEY-I' NrrE STATS r MORRISE. LEEDS, OF PHILADELPHIA, PENNSYEVANIA.

liIEASUR ING APPARATUS.

"Specification oflIietters Patent. Patgnt gfl play 26, 1914 Application filed November 18, 1912. Serial No. 731,935.

I ing is a specification.

My invention relates to electrical measuring apparatus involving the principle of the Wheatstone bridge.

My invention resides in apparatus of this character which may be used for the measurement of resistance generally, and which is particularly adaptable to the measurement of temperature, based upon the change in resistance of a conductor with change in temperature. And my invention resides further in apparatus of this character in which leads or conductors extending from the main part of the apparatus to the unknown resistance, such as a thermometer resistance, are so related, as hereinafter described, as to introduce no error into the determinations made by means of the apparatus. And it is a further feature of my invention, in this relation, to so employ relatively movable contacting parts that the contact resistance introduces no error into the determinations made by the apparatus.

My invention resides in the features hereinafter described and claimed.

For an illustration of one of the forms my invention may take, reference is to be had to the accompanying drawing, in which:

Figure 1 is a diagrammatic view illustrating the circuits and parts of my apparatus. Fig. 2 is a view illustrating an example of means for moving the movable contacts in unison.

Referring to Fig. 1, A and B represent resistances in the ratio arms of a Wheatstone bridge and R and T represent resistances in the other arms of the bridge, the former, R, a known resistance and the latter, T, representing the unknown resistance, or, in the case of temperature measurement, the resistance of a resistance thermometer. Between the bridge arms including the resistances R and A is connected the resistance w extending from the point 1 to the point 2, this resistance w taking any suitable form, here illustrated as a straight slide wire resistance. Engaging and adapted to traverse this resistancew and to shift the point of junction between the bridge arms including resistances R and A is a movable contact forming one terminal of a con jugate conductor 3 whose other terminal is at 4 at the junction of the bridge arms con taining the resistances B and T, the com ductor 3 including a galvanometer or other suitable indicatin instrument G. And connected between the bridge arms including the resistances A and B is a-second slide wire or similar resistance to extending from point 5 to point 6, the resistance "211 being engaged and adapted to be traversed by the sliding contact it forming one terminal 0 the conjugate conductor 7 whose other terminal is at the point 8 at the junction between the bridge arms including the resistances R and T. The position of contact 71.

determines the point of junction between the bridge arms including the resistances A and B. The conductor 7 terminates in the apparatus itself at the binding post 9 from which extends the lead 10 to the point 8, the lead 10 being in effect a part of the conjugate conductor 7. Connected in this conjugate conductor 7 is a battery or other source of current C and a switch or key which when depressed engages the. contact point llto close the normally open circuited conductor 7. 12 and 13 represent binding .posts to which are connected the thermometer leads L, one in each of the bridge arms including the resistances It and T. These leads L are of equal resistances, and since they extend irom the bridge apparatusproper to the more or less distant thermometer resistance T, are preferably made of the samelength of conductor, of the same material, and of the same cross section. The leads L, and the lead or conductor 10 may be disposed in a cable, or in a braid or twist, the etiect being, as to the leads L,'L that they are subjected to the same temperatures throughout their lengths and therefore continue to exhibit equal resistances.

t is necessary that the resistances in the bridge armsi-ncluding the resistances A and B shall at all times be equal to each other in order that the leads L, L may rigidly compensate each other and introduce no error. This follows from the equation for the Wheatstone bridge as follows:

o c+L am (1) Where a is the resistance of the bridge arm including the resistance A; Z) the resistance c+L=d+L 2 and this can only be true when azb (3) It is accordingly a necessary condition that the resistance in the ratio arms of the bridge shall be equal to each other, if the bridge apparatus is to be used to measure a resistance at a distance where lead wires are necessarily used, and these leads or lead wires are not to afi'ect the accuracy of the measurements.

Where the thermometer-or other resistance T is of relatively low value, or where the resistance of T varies through a small range, it is not desirable to. balance the bridge by changing the amount of the resistance R by means of a contact slidingon it and in series with R in the same arm of the bridge, since the resistance of the contact itself may be large enough to introduce an error. It is desirable to efi'ectthe balance of the bridge by shifting contacts which cannot introduce any contact resistance into the bridge arms. Accordingly I efi'ect the balance of the bridge by one or more of the sliding contacts, as g and h, associated with the conjugate conductors, contact resistance between these sliding contacts and their cooperating resistance conductors introducing no change in resistance, so far as contacts are concerned, into the bridge arms.

I accomplish the two results desired,

' namely the maintenance of unity ratio between the arms including resistance A and B and the balancing of the bridge without introducting contact resistance into any of the bridge arms by the arrangement shown in Fig. 1. i I

Forthe purposes of illustration let itbe assumed that the resistance w consists of 1,000 units of resistance, each unit having a resistance r. The resistance of the slide wire or other conductor 10 has a resistance onehalf that of resistance conductor '11). 7 Accordingly let it be flSSLLIIlGd that the resistance conductor w has a resistance of one thousand (1,000) units, each unit being of a 1' res stance 2 By mechanical construction, hereinafter described, the'two movable contacts 9 and it move in unison with each other so that when the contact 9 is at point 1 the movable contact h will be at point 5, and when the movable contact g is half way along the conductor w, that is, mid-way between points 1 and 2, the movable contact it will be onehalf Way along the conductor w that is, mid way between the points 5 and 6. And in constructing the apparatus the resistances A, 10 and B are made such that The bridge equation now becomes:

which is unity, as stated above to be a necessity.

Then since the first member of equation (5) is unity we have:

R m" L Y 1 'l If (7) from which follows:

T=R+nr (8) I and n: T R (9) Centigrade.

As stated above, the movable contacts 9 and h are moved in unison over their cooperating resistance condu ctors 'w and 'w respectively. This may be accomplished as indicated in Fig. 2 where the contacts 9 and h are secured to the same member 14, and insulated from each other. The member 14: is movable by handle 15 backwardly and forwardly in the direction of theconductors wand" 10 A scale'lfi may beprovided with which cotiperates'a pointer 17 movable with the member 1a; This scale may be cali brated in any desired units, such as resisteance units, temperature units, or empirical units.

T have si'iown'in' s'hunt to the conductors to and w the resistances S and S respectively; These are employed tosecure between the points 1 and 2 and the polnts 5- and 6 the exactamount of resistance required. Tit conductors'w'and 10 are nototthe exact resistance required, the shunt resistances may be employed of the rightamount to secure-the proper resistances between thepoints land 52 and the'points 5 and;

6; in other'words Sand S are re'sistances for facilitating" adjustment of the resist ances, between the points named. However, it resistances w and'w are of correct values, the shunts S and Sinay be onutted;

The 0 eration of theapparatus is as f0llows: he'resistance T is placed in the at mosphere or material or mediumwho'se temperature is to be measured: and on attaining such temperature exhibits a certain resistance. The cont'acts'g and it are moved by handle 15 backwardly' and forwardly along the- Wires w and w? until, with the key it in engagement with conta'ctil, the galvanometer or other inst-rumentGr indicates. no current flow in the conductor 3, in which Thenthe case the bridge is in balance. reading of'the' scale for the positions-f the pointerl'? is taken andif'the scale is callbrated in temperature units, the temperature is read directlyfromthe scale. Or if thescale bedivided into resistance units the resistance change otthe resistan'ce"T is" read or determined'tromthe scale, in ac-' cordancewith'equation (8), and then from a caiib'ration curve of theresistanceT;a the temperature correiponding to the determined resistance 0' "T is readofl. lit is to be understood that the source of curl-enter bzuttery U andthe gaivan'ometer or-indicat 7 ing instrument 'Grrnay' be interchanged" by' moving contact 9 toward point 2, resistance is" simultaneo-usiy removedfrom" the (ratio arm including resistance A and resistance introducedat one' half the rate into-the same a l ratio arm by' movement' of contact 72; to

. ward point 6. And simultaneously resistance" isbeingremoved from" the ratio arm lIICliHCiIDg IBSISlEB/QI'CG B'.- And the resistance And instead of the arm including the resistance T is va-' ried only by the change" in-the resistance of T due to temperature changes; and that whatever changes occur'in' the resistance of the leads L, lb, due to temperature changes; their effects are canceled and have no effect upon the accuracy of the measurement.

What I claim is: V

l. The combination" with a Wheatstone bridge'and its source of current and galvan'ometer, of a resistance intervening be tween the ratio arms of said bridge, a'sec- 0nd resistance intervening between one of said" ratio arms and a thirdarm of said bridge, and means for adjusting terminals of conjugate conductors of said bridge with respect to said intervening resistances for maintaining.- fixed the ratio bfiiJWGGIlftilB resistances ofthe ratio arms of said bridge:

2. The combination with a Wheatstone bridge and its source of'current" and galvanometer, of a resistance intervening between the-ratio' arms 'ot'said bridge, a second resistance intervening between one" of said ratio arms and a thirdarm'of said bridge, and means-for adjusting terminals of conjugate conductors-oi said bridge with respect to said intervening resistances for maintaining equality between the resistances of said ratio arms.

3. The combination with a Wheatstone bridge and its source" of current and galvanometer of a resistance" intervening be: tween the ratio arms'oit said-bridge, a second resistance intervening: between one of said ratio arms and a thirdarm of said bridge, and meansfor adjusting terminalsof con jugate conductors ofsaidbridge with respect to said intervening resistances for changing said first named-intervening resistance at onehalf' the 'rateof change oisaid second interveningresistance.

a. The combination with a Wheatstone bridge and" its source (it-current and galvanomet'er, of a resistance intervening be-' tween the'ratlo armsfot said bridge, a' second resistance lntervenmgl between i one of said' ratio arms" and a third arm" of" said' bridge and a thirdarm of said bridge, contacts forming terminals of the conjugateconductors of said bridge, and means for causing relative movement between said contacts and said intervening resistances in unison.

6. The combination with a WVheatstone bridge and its source of current and galvanometer, a resistance intervening between the ratio arms of said bridge, a resistance intervening between a ratio arm of said bridge and a third arm of said bridge, contacts forming terminals of the conjugate conductors of said bridge, and means for causing relative movement between said contacts and said intervening resistances in unison, the ratio of the resistances in said ratio arms remaining constant for all adjustments of said contacts with respect to said intervening resistances.

7. The combination with a Wheatstone bridge and its source of current and galvanometer, a resistance intervening between the ratio arms of said bridge, a resistance intervening between a ratio arm of said bridge and a third arm of said bridge, and means for causing relative movement between said contacts and said intervening resistances in unison, the ratio of the resistances in said ratio arms remaining unity for all adjustments of said intervening resistances.

8. The combination with a lVheatstone bridge and its source of current and galvanometer, a resistance intervening between the ratio arms of said bridge, a resistance intervening between a ratio arm of said bridge, and a third arm of said bridge, and means for causing relative movement between said contacts and said intervening resistances in unison, a given relative movement between said contacts and intervening resistances producing double the change of resistance in said second intervening resistance that is produced in said first intervening resistance. 4

9. The combination with a Wheatstone bridge and its source of current and galvanometer, of a resistance intervening between the ratio arms of said bridge, a sec- 0nd resistance intervening between a ratio arm of said bridge and a third arm of said bridge and having a resistance value twice that of said first named resistance, contacts forming terminals of the conjugate conductors of said bridge, 'and means for moving said contacts in unison with respect to said intervening resistances.

10. The combination with a Wheatstone bridge and-its source of current and galvanometer, of means for maintaining the ratio-of the resistances in the ratio arms of said bridge at unity comprising resistances intervening between different arms of said bridge, and contacts forming terminals of the conjugate conductors of said bridge traversing said intervening resistances in unisonr 11. The combination with a Wheatstone bridge and its source of current and galvanometer, of means for maintaining the ratio of the resistances in the ratio arms of said bridge at unity comprising resistances intervening between different arms of said bridge, and contacts forming terminals of the conjugate conductors of said bridge traversing said intervening resistances in unison, an unknown resistance and a lead in one arm of said bridge, a second lead in another arm of said bridge, said leads being of equal resistances, and a third lead in a conjugate conductor of said bridge.

12. The combination with a Wheatstone bridge and its source or" current and galvanometer, of an unknown resistance and a lead in one arm of said bridge, a resistance and a second lead in another arm of said bridge, said leads being of equal resistances, a resistance intervening between the ratio arms of said bridge, a resistance intervening between one of said ratio arms and the arm ,of said bridge including said second lead, contacts forming terminals of the conjugate conductors of said bridge, and means for moving said contacts in unison with respect to said intervening resistances.

13. The combination with a /Vheatstone bridge and its source of current and galvanometer, of fixed resistances in the ratio arms of said bridge, a resistance intervening between said ratio arms, the fixed resistance in the first ratio arm plus said intervening resistance equaling the fixed resistance in the second ratio arm, and a second resistance intervening between said first ratio arm and a third arm of said bridge, said second intervening resistance having twice the value of said first named intervening resistance.

14. The combination with a Wheatstone bridge and its source of current and galvanometer, of.fixed resistances in the ratio arms of said bridge, a resistance intervening between said ratio arms, the fixed resistance in the first ratio arm plus said intervening resistance equaling the fixed resistance in the second ratio arm, a second resistance intervening between said first ratio arm and a third arm of said bridge, said second intervening resistance having twice the value of said first named intervening resistance, contacts forming terminals of the conjugate conductors of said bridge, and means for moving said contacts in unison with respect to said intervening resistances.

15. The combination with a Wheatstone bridge and its source of current and gal vanometer, of an unknown resistance and a lead in one arm of said bridge, a resistance and a second lead in another arm of said bridge, said leads being of equal resistances, resistance adjusting means for maintaining the ratio of the resistances in the ratio arms of said bridge at unity comprising resistances intervening between difierent arms of said bridge, and contacts traversing the same and forming terminals of the conjugate conductors of said bridge, and a scale associated with said resistance adjusting means, said scale giving a reading when said bridge is balanced determinant of said unknown resistance.

16. The combination with a Wlieatstone bridge and its source of current and galvanometer, of an unknown resistance and a lead in one arm of said bridge, a resistance and a second lead in another arm of said bridge, means for balancing said bridge while niaintainin the resistance in the ratio arms of said bri ge at unity comprising resistances intervening between different arms of said bridge and contacts traversing the same and forming terminals of the conjugate conductors of said bridge, and a scale' associated with said balancing means, said scale giving a reading determinant of said unknown resistance when said bridge is balanced.

17. The combination with a Wheatstone bridge and its source of current and galvanometer, a slide wire resistance intervening between the ratio arms of said bridge, a second slide Wire resistance intervening between one of said ratio arms and a third arm of said bridge, contacts forming terminals of the conjugate conductors of said bridge, and means for causing relative movement between said contacts and said slide wire resistances in unison.

In testimony whereof I have hereunto atiixed my signature in the presence of the two subscribing witnesses.

MORRIS E. LEEDS.

Witnesses:

CHAS. S. BEDDING, WM. M. C. KIMBER. 

